diff mbox series

[2/7] add default dummy 'runtime constant' infrastructure

Message ID 20240610204821.230388-3-torvalds@linux-foundation.org (mailing list archive)
State New
Headers show
Series arm64 / x86-64: low-level code generation issues | expand

Commit Message

Linus Torvalds June 10, 2024, 8:48 p.m. UTC 
This adds the initial dummy support for 'runtime constants' for when
an architecture doesn't actually support an implementation of fixing up
said runtime constants.

This ends up being the fallback to just using the variables as regular
__ro_after_init variables, and changes the dcache d_hash() function to
use this model.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 fs/dcache.c                         | 11 ++++++++++-
 include/asm-generic/Kbuild          |  1 +
 include/asm-generic/runtime-const.h | 15 +++++++++++++++
 include/asm-generic/vmlinux.lds.h   |  8 ++++++++
 4 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 include/asm-generic/runtime-const.h

Comments

Borislav Petkov June 12, 2024, 10:04 a.m. UTC | #1 
On Mon, Jun 10, 2024 at 01:48:16PM -0700, Linus Torvalds wrote:
> Subject: Re: [PATCH 2/7] add default dummy 'runtime constant' infrastructure

Probably need a subject prefix:

"runtime-const: Add default..."

> This adds the initial dummy support for 'runtime constants' for when
> an architecture doesn't actually support an implementation of fixing up
> said runtime constants.

...
diff mbox series

Patch

diff --git a/fs/dcache.c b/fs/dcache.c
index 8b4382f5c99d..5d3a5b315692 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -35,6 +35,8 @@ 
 #include "internal.h"
 #include "mount.h"
 
+#include <asm/runtime-const.h>
+
 /*
  * Usage:
  * dcache->d_inode->i_lock protects:
@@ -102,7 +104,8 @@  static struct hlist_bl_head *dentry_hashtable __ro_after_init;
 
 static inline struct hlist_bl_head *d_hash(unsigned long hashlen)
 {
-	return dentry_hashtable + ((u32)hashlen >> d_hash_shift);
+	return runtime_const_ptr(dentry_hashtable) +
+		runtime_const_shift_right_32(hashlen, d_hash_shift);
 }
 
 #define IN_LOOKUP_SHIFT 10
@@ -3129,6 +3132,9 @@  static void __init dcache_init_early(void)
 					0,
 					0);
 	d_hash_shift = 32 - d_hash_shift;
+
+	runtime_const_init(shift, d_hash_shift);
+	runtime_const_init(ptr, dentry_hashtable);
 }
 
 static void __init dcache_init(void)
@@ -3157,6 +3163,9 @@  static void __init dcache_init(void)
 					0,
 					0);
 	d_hash_shift = 32 - d_hash_shift;
+
+	runtime_const_init(shift, d_hash_shift);
+	runtime_const_init(ptr, dentry_hashtable);
 }
 
 /* SLAB cache for __getname() consumers */
diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index b20fa25a7e8d..052e5c98c105 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -46,6 +46,7 @@  mandatory-y += pci.h
 mandatory-y += percpu.h
 mandatory-y += pgalloc.h
 mandatory-y += preempt.h
+mandatory-y += runtime-const.h
 mandatory-y += rwonce.h
 mandatory-y += sections.h
 mandatory-y += serial.h
diff --git a/include/asm-generic/runtime-const.h b/include/asm-generic/runtime-const.h
new file mode 100644
index 000000000000..670499459514
--- /dev/null
+++ b/include/asm-generic/runtime-const.h
@@ -0,0 +1,15 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RUNTIME_CONST_H
+#define _ASM_RUNTIME_CONST_H
+
+/*
+ * This is the fallback for when the architecture doesn't
+ * support the runtime const operations.
+ *
+ * We just use the actual symbols as-is.
+ */
+#define runtime_const_ptr(sym) (sym)
+#define runtime_const_shift_right_32(val, sym) ((u32)(val)>>(sym))
+#define runtime_const_init(type,sym) do { } while (0)
+
+#endif
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 5703526d6ebf..389a78415b9b 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -944,6 +944,14 @@ 
 #define CON_INITCALL							\
 	BOUNDED_SECTION_POST_LABEL(.con_initcall.init, __con_initcall, _start, _end)
 
+#define RUNTIME_NAME(t,x) runtime_##t##_##x
+
+#define RUNTIME_CONST(t,x)						\
+	. = ALIGN(8);							\
+	RUNTIME_NAME(t,x) : AT(ADDR(RUNTIME_NAME(t,x)) - LOAD_OFFSET) {	\
+		*(RUNTIME_NAME(t,x));					\
+	}
+
 /* Alignment must be consistent with (kunit_suite *) in include/kunit/test.h */
 #define KUNIT_TABLE()							\
 		. = ALIGN(8);						\